Molecules Of Different Sizes Research Articles

The third virial coefficient of hard discs of different sizes

Explicit calculations are made of the third virial coefficient and of the corresponding term in the expansion of the pair distribution function for three discs or three square-well molecules of different sizes confined to a plane.

Plasmid-like properties of the four virulence-associated factors of Yersinia pestis.

The virulence-associated factors of Yersinia pestis, which determine the abilities to produce pesticin I (Pst+), capsular fraction I antigen (Fra+), V and W antigen complex (Vwa+) and a cell-surface component for adsorption of exogenous pigments (Pgm+), were independently eliminated by cultivation of the cells in the presence of acridine orange, ethidium bromide or sodium dodecyl sulfate at a subinhibitory concentration. A virulent Y. pestis strain, Yreka, harbored at least five extrachromosomal DNA molecules of different sizes. In these molecules, a novel 13-megadalton DNA which was cured concomitantly with the elimination of the Fra factor was found, in addition to the known species of 7 and 44 megadaltons which were lost with the conversions to Pst- and Vwa-, respectively. Although the conversion to Pgm- could not be correlated with the lack of any proper extra-chromosomal DNA, the factor was transmitted to Pgm- cells with the aid of self-conjugative RP4 plasmid. The cells acquiring the Pgm factor regained virulence for mice.

Noncytolytic terminal complement complexes may serve as calcium gates to elicit leukotriene B4 generation in human polymorphonuclear leukocytes.

Complement effects on human polymorphonuclear leukocytes (PMN) have generally been ascribed to the anaphylatoxin C5a, which induces degranulation, superoxide anion generation, migration, and cell aggregation via interaction with membrane receptors. We here report that complement activation on the surface of antibody-sensitized human PMN provokes generation of the potent lipid mediator leukotriene B4 (LTB4) in strict dependence on complement component C8, but in the absence of detectable C9. The kinetics of LT generation are rapid, comparable with those observed after challenge with the calcium-ionophore A23187. LTB4 release is a distinct event that is dissociable from cytotoxicity as assessed by lactate dehydrogenase (LDH) release (dependent on C9) and from superoxide generation (independent of C8 and C9). It is dose dependent on extracellular calcium and is not observed in the absence of calcium. It is inhibited by substances interfering with calcium-calmodulin function (trifluoperazine and W7), but not by blockers of physiologic calcium channels (nimodipine, verapamil, and D 888). Addition of purified C8 to cells bearing C5b-7 induces a severalfold increase in their passive permeability to 45calcium. Sieving experiments with the use of marker molecules of different sizes collectively indicate the existence of small hydrophilic channels consisting exclusively or predominantly of C5b-8 complexes, which allow passive transmembrane flux of small molecules with Mr less than 200. Thus, noncytolytic terminal complement complexes may serve as a biological bypass gate for calcium in PMN membranes, triggering the arachidonic acid cascade with generation of LTB4 at doses well below the threshold required to invoke overt cell damage.

Heats of immersion in monolayer adsorption from binary liquid mixtures on heterogeneous solid surfaces: Equations for excess isotherms and heats of immersion corresponding to condensation approximation and Rudzinski-Jagiello approach

Equations are developed, by means of the Rudzinski-Jagiello (RJ) approach, for excess isotherms and heats of immersion in monolayer adsorption from binary solutions composed of molecules of different sizes, on heterogeneous solid surfaces. The equations are then tested by analyzing experimental excess isotherms and heats of immersion for adsorption of three binary liquid mixtures on various soilds. With the same number of parameters, the obtained fits shows an essential improvement over the agreement obtained by Condensation Approximation (CA) approach. It is shown that CA approach may lead to a serious overestimation of monolayer capacity value. The RJ approach yields also a remarkably different picture of the nonideality of the adsorbed phase.

An isotherm equation for adsorption from binary liquid mixtures on solids involving surface heterogeneity and differences in molecular sizes of components and its numerical verification

An equation derived previously14 for adsorption from binary liquid mixtures composed of molecules of different sizes on heterogeneous solids has been reexamined. Verification of this equation by means of numerical simulation showed its applicability for describing the liquid adsorption onto weakly and strongly heterogeneous surfaces.

Dependence of resid processing selectivity on catalyst pore size distribution

In the hydroprocessing of resid, catalyst selectivity and the relationship between metals and sulfur distribution in the resid are key factors in achieving required product specifications. Using gradient elution chromatography as a method of analysis, we have found that catalyst pore size distribution can significantly affect selectivity for different metal and sulfur components in residua. A small pore catalyst was observed to be more selective for non-asphaltene sulfur and metals, while a large pore catalyst was found to be very selective for asphaltene metals and sulfur. This variation of catalyst selectivity is a result of the concentration of metals and sulfur in different portions of the resid. For typical Middle Eastern residua, about 70–75% of the sulfur was found to be present in low molecular weight less aromatic GEC fractions, while 95% of the metals were in highly aromatic high molecular weight fractions. Thus the variation of selectivity with pore size was found to result from concentration of the sulfur and metal species in molecules of different size.

Separation and analysis of lipoproteins by gel filtration

Publisher Summary The principal method used for separation of biological molecules by size is gel filtration or gel chromatography. This method is also sometimes termed molecular sieve chromatography. In theory, molecules of different size may also undergo some ion exchange or adsorption effects in addition to size separation during gel chromatography and this is probably true for lipoproteins. However, chromatographic separation of lipoprotein particles appears to occur primarily because of differences in size and the term gel filtration is used. The separation of lipoproteins by size is a useful and instructive technique that, when used under well-defined conditions, provides concepts and information about lipoprotein particles that are not readily apparent from other commonly used procedures. Separation of lipoproteins by agarose gel filtration offers several advantages over those of other techniques: (1) the procedure is gentle and nondestructive, (2) the size distribution of particles can easily be visualized during separation for comparison among samples, (3) the procedure is simultaneously preparative and analytical, and (4) the completeness of recovery after separation is high.

Phase equilibria in model mixtures of spherical molecules of different sizes

Phase boundaries have been calculated for model binary mixtures comprising spheres of different sizes, between which there are long-range attractive forces. Particular attention has been paid to the case in which the ratio of sizes is infinite. The systems show a wide variety of behaviour that includes liquid–liquid and gas–gas immiscibility and the formation of negative azeotropes. The model systems are shown to reproduce some of the behaviour of aqueous solutions of surfactants if it assumed that the large spheres are models of the micelles and the small spheres models of the solvent molecules.

Lysophosphatidylcholine and taurodeoxycholate increase stomach permeability to different-sized molecules.

The influence of lysophosphatidylcholine (LPC), taurocholate (TC), and taurodeoxycholate (TDC) on gastric mucosal permeability was studied in a rat experimental model, with different-sized polyethylene glycols (PEGs) in the 722-1206-dalton range as permeability markers. Gastric mucosal morphology was also studied by transmission electron microscopy. We found that 2.5 mM and 5 mM LPC and TDC, but not TC, caused an increase in the passage of PEGs across the gastric mucosa. LPC altered the permeability significantly more than did TDC. Morphologically damaged intercellular microvillous structures could be seen after LPC treatment, whereas no obvious changes could be seen after TC or TDC treatment. These findings indicate that LPC and TDC may damage the gastric mucosa and enable permeation of molecules in the 722-1206-dalton range. Molecules within this range could potentially be toxic or antigenic, and this therefore represents an aspect of interest in the pathology of enterogastric reflux. Furthermore, the results indicate that dihydroxy secondary bile acids (TDC) have a more pronounced effect on gastric mucosal permeability than trihydroxy primary bile acids (TC).

Passage of Molecules through the Wall of the Gastrointestinal Tract

We have studied the influence of lysolecithin on mucosal permeability to different-sized molecules in the distal part of the ileum. Using a rat experimental model, we determined the intestinal permeability to ethylene glycol (62 dalton), different-sized polyethylene glycols (634- to 1206-dalton PEGs), and dextran 3000, in the absence and presence of lysolecithin. We also examined the morphology of the ileal mucosa and determined the activity of brush border enzymes after deposition of lysolecithin in the gut lumen. We found that lysolecithin did not affect the absorption of ethylene glycol and had no influence on the activities of the enzymes. In contrast, lysolecithin enhanced the desquamation of enterocytes at the villous tips and increased the permeability to 634- to 1206-dalton PEGs and dextran 3000. These findings indicate that lysolecithin may facilitate the uptake of larger, potentially antigenic and toxic molecules in the distal ileum, although the underlying epithelial desquamation might have little or no influence on the absorption of small compounds.

Permeability of blood-brain barrier to various sized molecules.

We studied disruption of the blood-brain barrier (BBB) by acute hypertension and a hyperosmolar solution. The goals were to determine whether 1) disruption of the BBB occurs primarily in arteries, capillaries, or veins, and 2) transport of different-sized molecules is homogeneous or size dependent. Sprague-Dawley rats were studied using intravital fluorescent microscopy of pial vessels and fluorescein-labeled dextrans (FITC-dextran, mol wt = 70,000, 20,000, and 4,000 daltons). The site of disruption was determined by the appearance of microvascular leaky sites. Transport of different-sized molecules was calculated from clearance of FITC-dextran. During gradual hypertension and osmotic disruption, all leaky sites were venular. Rapid hypertension produced venular leaky sites and, in some experiments, diffuse arteriolar extravasation of FITC-dextran. Clearance of different-sized molecules was homogeneous during acute hypertension. In contrast, clearance of molecules during osmotic disruption was size dependent. The findings suggest that 1) venules and veins are the primary sites of disruption following acute hypertension and a hyperosmolar solution; 2) transport of different-sized molecules is homogeneous following acute hypertension, which suggests a vesicular mechanism; and 3) transport following hyperosmolar disruption is size dependent, which suggests that hyperosmolar disruption may involve formation of pores as well as vesicular transport.

Characterization 0f solid-liquid adsorption systems by using Gaussian energy distribution

Theoretical foundations of the isotherm equations derived for adsorption from binary liquid mixtures composed of molecules of different sizes on heterogeneous surfaces characterized by Gaussian energy distribution are discussed. On the basis of numerical simulation studies the correlation between adsorption parameters of the equations in question and the parameters of the Gaussian energy distribution are established. These studies allow characterization of the Gaussian-type adsorbents on the basis of excess adsorption data.

Attempting the prediction of an azeotrope and its x- y curve on the basis of the molecular parameters

Predicting whether a given binary mixture be an azeotrope or not, and if so, estimating the azeotropic properties has been attempted by the use of the molecular parameters of components relating to size, potential and shape. The coordination numbers for a mixture composed of molecules of different sizes play an important role in calculating the total energy of interaction. By introducing an empirical formula to express interaction between different kinds of molecules, a successful prediction has been made at more than 90% probability with 137 binary mixtures. The azeotropic boiling temperature and composition have also been calculated satisfactorily, although the x - y equilibrium curves are not as good as expected.

Contribution of Trypsin and Cholate to the Pathogenesis of Experimental Alkaline Reflux Esophagitis

Previous studies suggest that trypsin and bile salts are the causative agents in alkaline reflux esophagitis. However, their individual effects on the esophageal mucosa is relatively weak when used alone. Since these agents seem to have different sites of action in the esophageal mucosa, we have investigated whether they might have a synergic action when used in combination. Rabbit esophagus was perfused in situ with a test solution containing trypsin and cholate, alone or in combination, at pH 7.0. The severity of mucosal damage was assessed, using as indicators of mucosal integrity transmucosal potential difference, net flux of Na+, and mucosal permeability to two neutral molecules of different sizes, 3H-H2O and 14C-erythritol. Cholate (in its conjugated and deconjugated form) was chosen as the bile salt test agent, because it is quantitatively important but almost inert on the esophageal mucosa when used alone. The results indicate that trypsin significantly decreased potential difference and increased mucosal permeability to Na+, 3H-H2O and 14C-erythritol. Cholate and taurocholate had no influence on the mucosa when used alone, but cholate, especially in its deconjugated form, increased significantly mucosal damage caused by trypsin. The findings suggest that trypsin and bile salts do have a synergic effect on esophageal mucosa, which may have pathogenetic significance in clinical alkaline reflux esophagitis.

Können flüssige Mischungen durch die Gittertheorie nach Guggenheim beschrieben werden?

AbstractBy using perturbation theory it is shown that the lattice theory of Guggenheim applied to molecules of equal size makes good predictions for the excess Helmholtz energy aηE and the excess energy uηE for mixing at constant density. The differences of aηE and uηE to the excess quantities gpE and hpE for mixing at constant pressure, however, can be considerably large and are expressed analytically. These results are also essential for understanding new computer simulations. Finally, the applicability of the lattice theory to molecules of different sizes is investigated.

Local composition in liquid mixtures

Nonrandomness and local compositions in model liquid mixtures have been investigated by computer simulation (molecular dynamics) and perturbation theory. The computer simulation represents nonrandomness due to both attractive and repulsive forces, whereas perturbation theory is restricted to the effect of repulsive forces (size differences). In the case of mixtures of equal-sized molecules, the quasichemical approximation of Rushbrooke and Guggenheim gives good results concerning both the magnitude of the effect and its concentration dependence. For a quantitative description, some corrections are necessary for the difference in coordination number around strongly and weakly interacting molecules. Perturbation theory neglects the effect of nonrandomness. However, as emphasized by Rushbrooke and Guggenheim, this effect is not of great thermodynamic significance. For mixtures of molecules of different sizes, packing effects (included in perturbation theory) are dominant, and may be of opposite sign to the effect caused by attractive forces.

Heterogeneity of plastid DNA of two species of brown algae

The plastid DNA of two filamentous marine algae Pylaiella littoralis (L.) Kjellm. and Sphacelaria sp. is composed of circular molecules of different sizes which have been visualized by electron microscopy. The absence of mitochondria in the plastid pellets as seen from electron micrographs as well as the absence of activity of three mitochondrial enzymes exclude the possibility of a mitochondrial origin of these molecules. The Sphacelaria plastome contains circular molecules ranging from 31 μm to more than 50 μm; the Pylaiella plastome contains circular molecules of 17.8 ± 1 μm (which are the smallest ones described so far in plastids), circular molecules of 37.9 ± 3 μm, and larger entangled DNA with two linear ends (whole length over 70 μm). Restriction endonuclease fragment analysis confirms the heterogeneity of the plastomes of both algae: the sum of fragment molecular weights gives much more than the molecular weight expected from the length of the smallest molecule.

The interpenetration of two chain polymers in a good solvent

The interpenetration of two excluded-volume chain molecules of different size in dilute solution is studied via scaling and renormalization methods. The chains are found to interpenetrate much more strongly than smoothed-density models suggest, in accordance with recent work by Khokhlov. The pair correlation funtion g(r) goes to zero at the origin only as a weak power of r. This power is related to Des Cloizeaux’s exponents ϑi describing intrachain correlations. The power is also related to the scaling exponents of star polymers. The mutual excluded volume MSL of two chains with greatly different length is proportional to the volume of the smaller chain and to the mass of the larger. Thus MSL is much smaller than a smoothed density model would predict. We discuss which chain correlations give rise to this small MSL. The universal coefficient relating MSL to the radius of gyration of the smaller chain is strongly dependent on the dimension d of space, according to our second-order expansion in 4-d. The interpenetration behavior predicted here affects measurable thermodynamic, scattering, and physical–chemical properties of the solution.

Transposon Tn 3-mediated replicon fusion

To investigate inter-replicon transposition of Tn3, we used the cosmid-phage λ packaging system coupled with density gradient fractionation and isolated recombinant molecules of different sizes. Cosmids derived from ampicillin-resistance-transducing phage were classified into four groups: (1) cosmid-Tn3 donor cointegrates considered as Tn3 transposition intermediates, (2) similar cointegrates carrying deletions of one copy of Tn3 and of adjacent cosmid DNA sequences, (3) cosmids carrying a single Tn3 insertion, and (4) cosmids carrying two independent Tn3 insertions. Genetic and biochemical studies indicated that cosmids isolated from ampicillin-resistance transductants were derived from the authentic cosmid-Tn3 donor cointegrate intermediates.

Role of luminal H+ in the pathogenesis of experimental esophagitis.

The pathogenesis of acidic reflux esophagitis was investigated in an experimental model with special emphasis on the role of lumen-to-mucus diffusion of H+ in the pathogenetic mechanism. Esophageal damage was produced by perfusing an isolated segment of rabbit esophagus in situ with three injurious endogenous secretions of the upper gastrointestinal tract (taurocholate, 10 mM; pepsin, 2500 U/ml; lysolecithin, 2 mg/ml) with and without acid (HCl, 10 to 150 mM). The severity of mucosal damage was assessed using as indicators of mucosal integrity transmucosal potential difference, net flux of Na+, and mucosal permeability to two neutral molecules of different sizes--3H-H2O and 14C-erythritol. The data indicate that although the presence of luminal acid is needed for mucosal damage to develop, there is no relationship between the severity of the damage and the magnitude of the lumen-to-mucosa diffusion of H+. Even markedly increased diffusion of H+ alone, induced by an unphysiological high concentration of luminal acid (300 mM HCl), had only a minor influence on mucosal integrity, whereas all three test agents were able to cause severe mucosal damage in association with much lower rates of H+ diffusion. Furthermore, the severity of the mucosal damage caused by an individual test agent was not dependent on the HCl; concentration used (and hence on the magnitude of lumen-to-mucosa diffusion of H+). The data suggest that esophageal mucosal damage caused by taurocholate, pepsin, or lysolecithin in the presence of luminal acid is due to the direct action of the agent itself rather than to excessive accumulation of luminal H+ into the mucosal tissue.